This disclosure relates in general to a semiconductor device, and more particularly to a gate structure and method of forming a gate structure of a semiconductor device. Atomic layer deposition (ALD) and chemical vapor deposition (CVD) are two conventional technologies that have been used to form metal gate structures. However, after the metal layer is formed using the foregoing technologies, the pFET/nFET aperture may be narrow as a result of thick sidewalls formed during deposition of the metal layer.
During pFET processing, the narrow aperture can affect subsequent flow of metal-fill into the aperture. As the size of the semiconductor device decreases, the narrow width of the aperture becomes more of an issue (e.g., devices scaled below N28). Furthermore, with respect to nFET processing, once the metal layer has been formed, it may be desirable to remove a portion of the metal layer from the nFET. However, the aperture may be too narrow to allow efficient flow of metal removal solution therethrough. Thus, because of the narrow apertures that result from the use of ALD and CVD processes, ALD and CVD have not been satisfactory for the above reasons.
Physical vapor deposition (PVD) is another metal gate formation technology. The parameters of PVD operation may be more finely tuned and controlled (e.g. vertical and horizontal deposition rate), and can facilitate the formation of a metal layer that has an aperture that is larger than the apertures produced using ALD and CVD processes. Another disadvantage of ALD and CVD technologies is that they are conformal to the trench, and thus the thickness of sidewalls and bottom portions of the metal layer cannot be controlled. However, such conditions may be controlled using PVD technology.
Despite the advantages of PVD technology, one unsatisfactory aspect of using PVD technology to form a metal layer is that PVD technology cause the formation of overhang portions along the top surface of the metal layer. The overhang may narrow the top surface of the aperture, thereby obstructing the flow of metal-fill and/or chemical solutions into the aperture. Consequently, conventional PVD techniques for forming a gate are also not satisfactory for the above reasons. Thus, there is a need for improving the gate formation process when using PVD technology.